1. Field of the Invention
The present invention relates to a method of joining superconducting wires using an oxide high-temperature superconductive material, and more particularly, it relates to a method of joining superconducting multi-filament wires with each other and a method of joining a superconducting multi-filament wire with a superconducting single-filament wire.
2. Description of the Background Art
In recent years, ceramic superconductors, i.e., oxide superconductors are watched as superconductive materials exhibiting higher critical temperatures. Among such materials, yttrium, bismuth and thallium superconductors, which have high critical temperatures of about 90 K., 110 K. and 120 K. respectively, are expected for practical use. In relation to such high-temperature superconductive materials, long superconducting wires have been developed for application to a cable, a bus bar, a power lead, a coil and the like.
As to junction of superconducting wires which are formed by oxide high-temperature superconductors covered with a stabilizing metal such as silver, Sato et al. U.S. Pat. No. 5,051,397 discloses a method using an alloy preferably containing a bivalent metal element belonging to the group IIA or IIB of the periodic table. According to this method, the alloy is interposed between superconducting wires and to join the wires with each other by brazing. This method brings a joint portion of low resistance. In the portions joined with each other through the alloy, however, resistance remains at the critical temperature of the oxide high-temperature superconductors. Therefore, this method is unsuitable for junction for holding a high critical current density or permanent current junction formed in a coil or the like.
In application of a superconducting wire, on the other hand, a multi-filament wire which is resistant against bending distortion is an extremely advantageous material. When such a multi-filament wire is applied to a coil or the like, identical or different types of wires must necessarily be joined with each other, while permanent current junction is required particularly in a permanent current coil.
In view of the aforementioned background, the present invention has been proposed noting junction of a superconducting wire using an oxide high-temperature superconductor.